Temperature correction of NMR relaxation time distributions

Abstract

A method includes generating a temperature-corrected nuclear magnetic resonance (NMR) measurement-derived value corresponding to a target temperature using a correlation model that is based on a difference between the target temperature and a sample temperature. The method also includes determining a formation property based on the temperature-corrected NMR measurement-derived value corresponding to the target temperature.

What is claimed is: 
     
       1. A method comprising:
 generating a set of correlation models, wherein each of the set of correlation models correlates temperature to one or more geometric mean values of an NMR relaxation time distribution, wherein each of the set of correlation models comprises a corresponding calibration performance value; 
 selecting a correlation model from the set of correlation models based on a comparison of calibration performance values; 
 generating a temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to a target temperature using the selected correlation model that is based on a difference between the target temperature and a sample temperature; and 
 determining a formation property of a subsurface formation based on the temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to the target temperature. 
 
     
     
       2. The method of  claim 1 , wherein each of the set of correlation models correlates temperature to a non-time measured formation property. 
     
     
       3. The method of  claim 2 , wherein the non-time measured formation property comprises at least one of a pore throat distribution, a micro porosity cutoff, a macro porosity cutoff, a porosity, a permeability, a pore volume threshold, a pore connectivity threshold, and a pore throat size. 
     
     
       4. The method of  claim 1 , further comprising:
 acquiring a plurality of calibration NMR relaxation time distribution values at a set of calibration temperatures, wherein generating the set of correlation models is based on the plurality of calibration NMR relaxation time distribution values. 
 
     
     
       5. The method of  claim 4 , wherein at least one of the correlation models comprises a linear relationship between a logarithm of the plurality of calibration NMR relaxation time distribution values and the set of calibration temperatures. 
     
     
       6. The method of  claim 4 , wherein generating the set of correlation models comprises removing outlier data values from the plurality of calibration NMR relaxation time distribution values based on a threshold distribution value. 
     
     
       7. An apparatus comprising:
 a nuclear magnetic resonance (NMR) tool; 
 a processor; and 
 a machine-readable medium having program code executable by the processor to cause the apparatus to, 
 generate a set of correlation models, wherein each of the set of correlation models correlates temperature to one or more geometric mean values of an NMR relaxation time distribution, wherein each of the set of correlation models comprises a corresponding calibration performance value; 
 select a correlation model from the set of correlation models based on a comparison of calibration performance values; 
 generate a temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to a target temperature using the selected correlation model that is based on a difference between the target temperature and a sample temperature; and 
 determine a formation property of a subsurface formation based on the temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to the target temperature. 
 
     
     
       8. The apparatus of  claim 7 , wherein each of the set of correlation models correlates temperature to a non-time measured formation property. 
     
     
       9. The apparatus of  claim 8 , wherein the non-time measured formation property comprises at least one of a pore throat distribution, a micro porosity cutoff, a macro porosity cutoff, a porosity, a permeability, a pore volume threshold, a pore connectivity threshold, and a pore throat size. 
     
     
       10. The apparatus of  claim 7 , further comprising program code to cause the apparatus to:
 acquire a plurality of calibration NMR relaxation time distribution values at a set of calibration temperatures, wherein the generation of the set of correlation models is based on the plurality of calibration NMR relaxation time distribution values. 
 
     
     
       11. The apparatus of  claim 10 , wherein at least one of the correlation models comprises a linear relationship between a logarithm of the plurality of calibration NMR relaxation time distribution values and the set of calibration temperatures. 
     
     
       12. The apparatus of  claim 10 , wherein the program code to generate the set of correlation models comprises program code to remove outlier data values from the plurality of calibration NMR relaxation time distribution values based on a threshold distribution value. 
     
     
       13. One or more non-transitory machine-readable media comprising program code for determining a formation property of a subsurface formation, the program code to:
 generate a set of correlation models, wherein each of the set of correlation models correlates temperature to one or more geometric mean values of an NMR relaxation time distribution, wherein each of the set of correlation models comprises a corresponding calibration performance value; 
 select a correlation model from the set of correlation models based on a comparison of calibration performance values; 
 generate a temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to a target temperature using the selected correlation model that is based on a difference between the target temperature and a sample temperature; and 
 determine the formation property of the subsurface formation based on the temperature-corrected geometric mean value of the NMR relaxation time distribution corresponding to the target temperature. 
 
     
     
       14. The machine-readable medium of  claim 13 , wherein each of the set of correlation models correlates temperature to a non-time measured formation property. 
     
     
       15. The machine-readable medium of  claim 13 , further comprising program code to:
 acquire a plurality of calibration NMR relaxation time distribution values at a set of calibration temperatures, wherein the generation of the set of correlation models is based on the plurality of calibration NMR relaxation time distribution values. 
 
     
     
       16. The machine-readable medium of  claim 15 , wherein at least one of the correlation models comprises a linear relationship between a logarithm of the plurality of calibration NMR relaxation time distribution values and the set of calibration temperatures. 
     
     
       17. The machine-readable medium of  claim 15 , wherein the program code to generate the set of correlation models comprises program code to remove outlier data values from the plurality of calibration NMR relaxation time distribution values based on a threshold distribution value.